Numerical Simulation of Precipitation in Yosemite National Park with a Warm Ocean: A Pineapple Express Case Study

Abstract

Precipitation from a warm winter, orographic storm during Christmas of 1996 in Yosemite National
Park and the Sierra Nevada was simulated with the NCAR mesoscale weather model called WRF.
The sea-surface temperature of the Pacific Ocean upwind of the mountains was prescribed to six
different fixed temperatures and the resulting simulated precipitation compared to the actual storm
precipitation. Warm sea-surface temperatures increased the precipitation above normal by as much
as a factor of four. Based on the likely increase in precipitation rate and frequency of storms following
the Genesis Flood, glaciers thousands of feet thick would have developed in a few hundred years.

Introduction

Vardiman (2008) proposed that a series of
numerical simulations of precipitation be conducted
in Yosemite National Park to determine if a warm
Pacific Ocean heated by the Genesis Flood could
explain the occurrence of glaciers for the Sierra
Nevada in a young-earth time frame. He suggested
that a conventional mesoscale meteorology model
available from the National Center for Atmospheric
Research (NCAR) be used to simulate precipitation
for several types of storms at multiple sea-surface
temperatures (SSTs). The first simulation to be
completed was a warm storm with a long, steady
fetch over the Pacific Ocean from near Hawaii called
The Pineapple Express. The specific storm reported
here occurred from December 26, 1996, to January 3,
1997.

General Storm Summary

The Pineapple Express storm is one class of storms
which affects the West Coast of the U.S. It consists
of a series of storms which travel along a persistent
atmospheric flow trajectory from the southwest. It
has its origin in the tropical Pacific, frequently near
the Hawaiian Islands and lasts from three days to
as long as three weeks. Some observers swear they
can smell pineapples on the wind during these events.
Although the smell of pineapples may be a bit of an
exaggeration, the warm, balmy air during a Pineapple
Express event is certainly pleasant and moisture
laden during normally cold winter storms. When the
warm air is lifted over the Coastal Range and the
Sierra Nevada along the West Coast, it precipitates
massive quantities of rain at low elevations and snow
at the high elevations. Often rain falling on snow that
has fallen earlier in the winter can cause disastrous
flooding along the rivers and lowlands of California,
Oregon, and Washington.

It is not uncommon for the total amount of
precipitation falling from a series of fronts embedded
in such storms to exceed the normal precipitation for
an entire season. The author was personally familiar
with such a storm that occurred during his tenure as
field director of the Sierra Cooperative Pilot Project,
a U.S. Department of Interior cloud seeding research
project, which dropped almost 30 feet of fresh snow
in the central Sierra Nevada near Lake Tahoe in less
than a month. The 20-foot tall towers on which rain
gages had been installed to measure snowfall in the
highest terrain were overtopped by the snow from
this single, month-long event.

The heavy precipitation event of December 26,
1996, to January 3, 1997 simulated in this case study
was a similar storm. A cool pre-Christmas storm
brought valley rain and several feet of mountain
snow to southwest Oregon, northern California, and
western Nevada on December 21 and 22, 1996. This
system set the stage for what would become one of
the most historical flood events to affect the region
in recent times. A summary of this storm event from
which much of the descriptive information for this
report is drawn was published online by the NOAA
California/Nevada River Forecast Center (Kozlowski
and Ekern 1997).

Fig. 1 shows the general trajectory of the air flow
and storm track over the eastern Pacific and the West
Coast of the U.S. for the period of the storm. An upper-level
high pressure area over the Aleutian Peninsula
and an upper-level low pressure area in the lower Gulf
of Alaska forced the polar jet stream southward to flow
parallel to the subtropical jet stream. This pattern of
strong flow from near Hawaii northeastward across
the West Coast of the U.S. persisted for most of the
period of the storm.

Sea-Surface Temperature

Fig. 2 shows the distribution of sea-surface
temperature over the eastern Pacific Ocean during the
Pineapple Express case. The sea-surface temperature
of the yellow region over which much of the air
flowed before reaching the West Coast for the actual
case averaged about 20°C. The source region for the
air near Hawaii approached 30°C. The sea-surface
temperature was colder close to the coastline because
of the clockwise ocean circulation in the Pacific gyre
which brings southward some of the colder 10°C
water in Gulf of Alaska. The distribution of sea-surface
temperature for the simulations was more
homogeneous than the actual storm case shown here.

Precipitation

Beginning on Christmas Eve, the overall weather
pattern over the Western U.S. began to shift from a
polar air mass toward a warmer and wetter tropical
regime with promise of a noteworthy precipitation
event. Not only would the relentless precipitation
through early January 1997 bring widespread
flooding, but the snow pack from the pre-Christmas
storm would significantly melt to exacerbate problems
from the otherwise large amounts of runoff. In
the series of tropical air mass storms for this case,
precipitation fell across much of the West Coast.
The Oregon Climate Services (Gibson, Taylor, and
Weisberg 1997) created a graphical re-analysis of
the precipitation for the period of December 29, 1996
through January 3, 1997 as shown in Fig. 3. This
storm was unique because of the widespread nature
of the precipitation footprint.

Fig. 2. Distribution of sea-surface temperature in the eastern Pacific for the Pineapple Express case.
SST in degrees Kelvin

Excessive precipitation fell over the higher terrain
from western Washington southward to northern
California and western Nevada. Although the
heaviest precipitation for this event was northward of
Yosemite National Park, considerable precipitation fell
there as well and the air flow over the Sierra Nevada
which produced the precipitation was strong even into
Southern California. In the simulation study to be
described later, the flow over Yosemite was more than
sufficient to process and precipitate large quantities
of water vapor evaporated from warm sea-surface
temperatures.

As the precipitation began to dissipate on January
3, 1997, the 9-day period showed amounts surpassing
40 inches in the Feather River Basin in northern
California. Elsewhere across the higher terrain of
northern California, amounts ranged from 15 to 30
inches. Between 14 and 18 inches of precipitation fell
at the highest elevations along the Sierra Nevada
near Yosemite National Park. Table 1 shows selected
precipitation totals in California for the 6-day and
9-day periods ending January 3, 1997.

Numerical Simulation of the Pineapple Express

Fig. 3. Total precipitation for the Western U.S. from December 29, 1996 through January 3, 1997 (Gibson, Taylor,
and Weisberg 1997).

Vardiman originally proposed simulating storms
in Yosemite using the NCAR Mesoscale Meteorology
Model (MM5) (NCAR 2003). However, by the time
the project began in the Fall of 2008 a new model
called the Weather Research and Forecasting Model
(WRF) (NCAR 2007) was available with updated
capabilities. It is based on similar procedures as
MM5 and contains many of the same subroutines.
It was decided to use the WRF model for the project
rather than the older MM5 model because it has more
capabilities and is actively supported.

WRF was installed on the EPIPHANY 44-node
parallel processor at the Institute for Creation
Research offices in Dallas, Texas, in the fall of 2008.
Wes Brewer developed the support software for
inputting and storing the data needed for conducting
simulations at Yosemite. Topographic data for
the Western U.S. and meteorological data for the
Pineapple Express case were imported into the model.
These data were available from NCAR by exercising
subroutines within WRF.

Fig. 4 shows three spatial domains which were
established for simulations of the Yosemite cases, all
centered on Mt. Hoffmann, a 10,850 foot mountain
near the center of Yosemite National Park. The three
domains allow simulations to be conducted over
progressively larger areas with coarser resolutions.
The smallest domain has dimensions about 650 km
east/west and 500 km north/south and 3 km grid
spacing. The middle domain is three times as large
as the inner domain with dimensions about 2,000 km
east/west and 1,500 km north/south and a grid
spacing of 9 km. The largest domain is nine times
as large as the innermost domain with dimensions
about 5,600 km east/west and 4,400 km north/south
and grid spacing of 27 km. Total storm precipitation
in millimeters is displayed by color. The precipitation
shown for a sample case in Fig. 4 varied from 0 to over
720 mm (~28 inches).

Validation of WRF for Pineapple Express

WRF has numerous subroutines and parameters
which can be activated and adjusted for various
conditions. For example, some of the cloud
physics subroutines are appropriate for
cold, winter storms and others for warm
tropical storms. Turbulence and mixing
can be adjusted in the dynamics portion
of the model. Various radiation codes are
available and boundary conditions can
be modified. Normally, these subroutines
and parameters are adjusted until
the computed precipitation from WRF
matches the observed precipitation.

The validation method used in the
Pineapple Express case study was
to set the various parameters in the
WRF model according to the conditions
expected in winter, orographic storms
and compare the computed total storm
precipitation with the observed total
storm precipitation. Fig. 5 shows a
comparison between the computed and
actual storm total precipitation for the
Pineapple Express case. Table 2 provides
additional information for the stations
shown on the graph.

The stations in the lower left corner of the graph
are generally in the Sacramento Valley at lower
elevations and upwind of the Sierra Nevada. The
stations in the upper right hand corner are typically
at higher elevations and in the mountains, although
there are several exceptions. The observed and
computed precipitation amounts both tend to increase
with altitude, but the relationship is not exact. The
regression coefficient between computed and observed
total storm precipitation was 0.822. This means that
approximately 68% of the observed precipitation over
the Sierra Nevada was explained by the WRF model.

This is a good correlation for precipitation
measurements, but not excellent. Most efforts to
predict precipitation show similar correlations.
Fluctuations in cloud coverage throughout a storm
and variations in precipitation efficiency often
introduce noise in such statistical comparisons. And
topographic variation as a function of wind speed
and direction relative to the gages, flow patterns, and
turbulence also cause large differences in computed
and observed precipitation in a gage network with
small numbers of instruments. This correlation was
judged to be adequate for the purposes of this study.

Table 1. Selected precipitation totals for 6-day and 9-day periods of
the December 26, 1996 through January 3, 1997 storm in California.

Numerical Simulation of Precipitation for Various Sea-Surface Temperatures

The Pineapple Express storm was simulated
with the WRF model for six different sea-surface
temperatures for the Eastern Pacific Ocean (0°C,
10°C, 20°C, 30°C, 40°C, and 45°C). The purpose was
to determine the effect of sea-surface temperature on
total storm precipitation in Yosemite National Park.
An attempt was made to complete a simulation at
50°C as well, but WRF became unstable and would
not complete a run at that temperature even with
very small time increments and long runs. The
maximum sea-surface temperature possible was
at 45°C, for consistent results with moderate time
steps and run times. One of the reviewers offered the
comment that when running models such as WRF,
the parameters are usually adjusted to work well
within the range of normally observed temperatures.
When sea-surface temperature rises to 30°C or above,
the parameters of the model may not be adjusted to
such hot temperatures and therefore, one can get
spurious results. But, this probably did not happen,
as the results seem logical and as expected with such
hot sea-surface temperatures. I agree with these
comments.

Fig. 4. Three spatial domains established for the simulation of storms in Yosemite National Park. The colored
regions represent total storm precipitation in millimeters. This display is the actual storm accumulation for
eight days of the Pineapple Express case.

The total 8-day precipitation for the smallest
domain is shown in Figs. 6–11 for sea-surface
temperatures from 0°C to 45°C. The Pacific Ocean
upwind of the California coast was maintained at
a constant sea-surface temperature throughout
each of the simulations. Note, in Figs. 6–11, the
California coastline is shown in the lower left-hand
corner of the diagram, the 120° west longitude line
(the northeastern border of California) is shown as
a dashed, vertical line near the middle, Lake Tahoe
is near the top center, and the boundary of Yosemite
National Park is shown to the right of the vertical
dashed line near the center of the plot.

The size scales of the diagrams are shown in
kilometers (km) along the horizontal and vertical
axes. The coastal range parallels the California coast
about 15 miles inland and varies in elevation from a
few hundred feet to a few thousand feet in Southern
California. The Sierra Nevada also parallels the
California coast, but is located about 150 miles inland
and varies in elevation from less than 4,000 feet north
of Los Angeles to over 14,000 feet at Mt. Whitney
south and east of Yosemite National Park. The ridge
line along the Sierra Nevada near Yosemite National
Park is generally between 10–12,000 feet.

East of the Sierra Nevada the elevation drops to
about 5,000 feet between north-south ridges over the
deserts of eastern California, Nevada, Utah, and
Arizona. The total precipitation is shown in various
shades of color with the color code displayed in
millimeters (mm) beneath each figure. The color codes
are different for each diagram in order to display the
greatest detail.

For the colder temperatures the precipitation
patterns show a close relationship between
precipitation and the location of mountains. The
heaviest precipitation occurred in the Sierra Nevada.
At warmer sea-surface temperatures the precipitation
seemed to be more controlled by the location of
the coast line. The precipitation was more widely
distributed over the entire region and less dependent
upon elevation.

The precipitation varied from a low of 30 mm (~1
inch) for a sea-surface temperature = 0°C in the San
Joaquin Valley upwind of the Sierra Nevada and in
the desert to the east to a high of 2,200 mm (~87
inches) for a sea-surface temperature = 45°C along the
coast. The maximum precipitation at the warmest sea-surface
temperatures displayed along the coast range
was not expected. The precipitation over the Sierra
Nevada was expected to increase monotonically with
warmer sea-surface temperatures. However,
precipitation over the Sierra Nevada increased
with sea-surface temperature from 0 to about
20°C, then decreased slightly at 30°C before
once again increasing at higher sea-surface
temperatures.

When precipitation in the Sierra Nevada
temporarily declined at 30°C, precipitation
along the coast range increased dramatically
and the valley precipitation upwind of the
Sierra Nevada began to increase. It appears
that sea-surface temperatures 30°C and
warmer over the Pacific Ocean caused
convection to break out over the ocean and
along the coast. At even warmer sea-surface
temperatures precipitation over the ocean and
along the coast exceeded precipitation along
the Sierra Nevada. Precipitation also became
greater over the Sierra Nevada for warmer sea-surface
temperatures, but not to the degree of
that at the coast.

Table 3 shows a coarse summary of the variation in
precipitation as a function of sea-surface temperature
and location. The total storm precipitation in the
Sierra Nevada increased from about 500 mm by a little
over a factor of about 3 to 1700 mm as the temperature
increased from 0°C to 45°C with a slight plateau at
30°C. The valley precipitation upwind of the Sierra
Nevada increased from 30 mm monotonically by a
factor of about 50 over the temperature change from
0°C to 45°C. The coastal precipitation increased from
80 mm monotonically by a factor of about 25 for the
same temperature change.

Precipitation Along a Line Perpendicular to the Sierra Nevada

Fig. 12 shows the mid-size model domain with
a line 60° relative to north perpendicular to the
Sierra Nevada. Fig. 13 shows the precipitation for
the Pineapple Express storm from southwest to
northeast along the 60° line centered on Mount
Hoffman in Yosemite National Park as a function
of sea-surface temperature. The 60° line is parallel
to the average flow of air over the mountain in the
Pineapple Express storm although the flow is more
southerly near the surface and more westerly aloft.
The 60° line runs from off the coast of Southern
California near Monterey, across the Sierra Nevada
into Nevada and Utah just south of the Great Salt
Lake, ending near Lander, Wyoming. The main peaks
in precipitation from left to right are caused by the
Coastal Range near the California coast, the Sierra
Nevada in eastern California, the Wasatch Range in
central Utah, and the Wind River Range in the Rocky
Mountains. The set of peaks in precipitation at the
left end of Fig. 13 occurs only for the 40°C and 45°C
sea-surface temperature and is due to convection over
the ocean.

Table 2. Station code, name, elevation, and computed and observed
precipitation for the Pineapple Express.

Station Code

Station Name

Elevation (m)

WRF Precipitation (mm)

Observed Precipitation (mm)

BKRF

Bakersfield

123

27.94

93.80

FRSN

Fresno

90

60.96

203.63

SACR

Sacramento

8

94.23

179.80

KAUN

Auburn

374

243.08

374.65

ATLP

Atlas Peak

826

468.38

199.77

CHLK

Chilkoot

2179

489.97

738.59

GASQ

Gasquet

116

503.94

455.81

SHDM

Shasta Dam

151

601.98

328.63

BLCN

Blue Canyon

1429

923.04

792.84

LAPR

La Porte

1518

1017.02

686.06

BULK

Bucks Lake

1573

1070.86

663.18

Notice that the precipitation increases with sea-surface
temperature over each of the mountain ridges.
It also increases more strongly at higher
temperatures. This will be discussed
more fully in the next section. Between
the mountain ridges the precipitation
remains relatively low, particularly
in the deserts of Nevada and Utah.
However, over the Pacific Ocean off
the coast of California the precipitation
increases strongly with sea-surface
temperature although there is no
orographic influence. This widespread
precipitation was noted earlier in the
horizontal displays of precipitation for
high values of sea-surface temperature
and is believed to be due to instability
over the warm ocean producing
convection. This instability also extended onto the
continent upwind and onto the coastal range and into
the Central Valley of California. Notice that at the
highest sea-surface temperatures the precipitation
increased uniformly all the way from the farthest
southwest to Mount Hoffman.

Accumulation of Precipitation in Yosemite National Park as a Function of Sea-Surface Temperature

Fig. 14 displays the accumulated WRF model
precipitation as a function of simulation time and sea-surface
temperature. The accumulated precipitation
shown here is the maximum precipitation at all
grid points within the Yosemite National Park
boundary shown in Figs. 6–11. The precipitation
accumulates more rapidly for the warmer sea-surface
temperatures indicating a higher precipitation rate
at warmer temperatures, as would be expected. The
WRF computed precipitation for the actual storm
(indicated as default) occurs between the 20°C and
30°C cases. This would be expected since the sea-surface
temperature for the actual storm averaged
about 22°C, although its sea-surface temperature
was not distributed homogeneously over the Eastern
Pacific like the other six cases.

Note, that the accumulation curves for the various
sea-surface temperatures do not increase regularly as
expected. For example, the 30°C accumulation curve
falls below the actual case and the 20°C curve between
about 125 and 175 hours before climbing rapidly back
to the expected order before the end of the storm. Why
the model does this is unclear. However, by the end of
the storm, the order of all sea-surface temperatures is
as one would expect.

The difference in the accumulated precipitation
is greater at higher temperatures, for example, the
difference is about 20 mm between 0°C and 10°C,
115 mm between 10°C and 20°C, 420 mm between
20°C and 30°C, 500 mm between 30°C and 40°C,
and 850 mm between 40°C and 45°C. This would be
expected since the rate of growth of snow in clouds and
the formation of precipitation should be proportional to
the water vapor available for cloud processes. But, the
amount of water vapor is an exponential function of
sea-surface temperature as governed by the Clausius-
Clapeyron equation. This is a well-known chemical-physics
equation that relates water vapor pressure in
air to the temperature of a nearby water surface.

According to this logic the accumulated precipitation
should be an exponential function of sea-surface
temperature. Under the same storm conditions, the
accumulated precipitation in Yosemite National
Park should be about two times greater at 30°C
than at 0°C and four times greater at 45°C than
at 0°C. Consequently, when the surface of the
Eastern Pacific is warm, large amounts of snow
will accumulate in the Sierra Nevada and when
it is cold only small amounts will accumulate, as
shown in Fig. 14.

Increased Glacier Growth

This study has shown that precipitation can be
doubled or even quadrupled in the Sierra Nevada if
the sea-surface temperature of the Pacific Ocean is
warmer. Such a large increase in precipitation would
readily lead to larger, more permanent glaciers if
the precipitation fell as snow. However, Pineapple
Express type storms occurring under warm sea-surface
temperatures could have a higher snow level.
That is one of the dangers of such storms today—the
likelihood of rain at high elevations falling on snow
producing flooding. Would a warm ocean cause the
snow level to be even higher than such storms of
today? If they did, then larger, thicker glaciers could be
eroded quickly under such conditions.
It seems likely that more rain will fall on the
Coastal Range of California and the foothills of
the Sierra Nevada under warmer sea-surface
temperatures, but snow will remain the dominate
precipitation type at higher elevations. Although a
warmer ocean will moderate the climate much as
it does today, it would likely extend its temperature
influence only a relatively short distance inland.
Today, this effect typically extends less than about
50 km inland. Mount Hoffman in Yosemite National
Park is about 200 km from the coastline. So, even if
the moderating effect of the ocean were doubled to
100 km, the region where most glaciers occur would
still be outside the direct warming influence of higher
sea-surface temperatures. Of course, Pineapple
Express type storms would still tend to produce rain
on snow as they do today and melt some of the snow.

One of the reviewers suggested a possible
mechanism for keeping the snow from melting in the
Sierra Nevada even with warm advection from the
Pacific. Volcanic aerosols in the stratosphere would
likely have been prevalent following the Genesis Flood
and would have kept the interior of the continents
cool, even in summer, and the Sierras would have
tended to have a cool low-level flow from the east. So,
as warm low pressure systems approached from the
west, winds from the east and southeast ahead of the
storm would have caused low-level air (below 12,000
feet above sea level) to spread into the Sierras. Warm
precipitation would start out as heavy snow (riding
over the cooler low-level air), change into freezing
rain, and then rain when the wind shifted out of the
west. But, the rain would simply be absorbed into the
snowpack, and as the effect of warm westerly winds
waned after a day or so, the water in the snow pack
would then freeze. So, volcanic aerosols would likely
be needed, especially in summer, to keep the snow
from melting at high altitudes.

Table 3. Total storm precipitation as a function of sea-surface
temperature and location.

Sea-Surface Temperature

(°C) Coastal Precipitation (mm)

Valley Precipitation (mm)

Sierra Precipitation (mm)

0

80

30

500

10

100

60

600

20

150

100

800

30

400

150

700

40

800

400

900

45

2200

1500

1700

An effect that was not modeled in this study is the
increased frequency of colder storms coming from
the northwest during ice age conditions. Crowley
and North (1991) have shown that the path of the jet
stream was positioned much further south during
the ice age—crossing from the Pacific Ocean onto the
North American continent near San Francisco. Such
a position would have caused the frequency of storms
crossing the Sierra Nevada to be increased greatly,
probably doubling the number of storms which
dumped rain and snow each winter. Furthermore,
the storms would probably have been colder due to
cold, polar air being displaced farther south. And
the winter season would have been extended into the
summer reducing the melting of glaciers. Multiplying
the two effects together—the increase in precipitation
due to warmer sea-surface temperatures and the
greater frequency of cold storms—it is likely that
the snowfall in the Yosemite National Park and the
Sierra Nevada in general, would have been four to
eight times what it is today and less of the glaciers
would have melted in the summer. A full assessment
of the difference in glacial growth must wait until
additional types of storm cases have been simulated,
but a crude estimate will be attempted here.

Fig. 12. Mid-size domain with a 60° line perpendicular to the Sierra Nevada. The colors indicate
total accumulated precipitation in millimeters. This display is for accumulated precipitation after
eight days for the actual Pineapple Express case.

Fig. 13. Precipitation for the Pineapple Express storm from southwest to northeast
along the 60° line in Fig. 12 centered on Mount Hoffman as a function of sea-surface
temperature.

Fig. 14. Accumulated WRF model precipitation in Yosemite National Park as a function of simulation time and sea-surface
temperature.

Fig. 14 shows that a Pineapple Express type storm
will precipitate a total of between 700 and 2,000 mm
per week depending upon sea-surface temperature.
Considering precipitation only from this type of storm
it is possible to calculate the depth of glaciers that will
accumulate in Yosemite National Park if no melting
occurs in the summers. For example, one Pineapple
Express type storm which precipitates
1,000 mm will contribute about 3.3 feet of
ice to a glacier. Snow would be five to ten
times greater in depth, but it would be
compressed to the density of ice over time.
The glacier thickness calculated here will
be for ice. If only one Pineapple Express
storm occurred each year, the glacier would
be 330 feet thick in 100 years. However, if
a Pineapple Express type storm occurred
every four weeks, the glacier would be over
4,000 feet thick in 100 years.

The WRF model computes precipitation in water equivalent millimeters, i.e., the depth of rain in millimeters or the depth snow would have in millimeters if it fell as rain. But, snow often initially has a density only 10% to 20% that of water. Snow is compressed by the accumulation of additional precipitation falling on the surface above. Its density increases to that of solid ice, eventually to about 90% that of water. Consequently, 1,000 millimeters of water equivalent precipitation in the form of snow that doesn’t melt will eventually contribute slightly more than 1 meter or 3.3 feet to the depth of a permanent glacier.

Fig. 15. Glacier depth as a function of precipitation rate and storm
frequency.

Fig. 15 shows glacier depth as a function
of precipitation rate and frequency of storms in
Yosemite National Park. Notice that glacier thickness
is a function of precipitation rate, frequency of storms,
and the length of an ice age. The blue oval in Fig. 15
represents an average condition which could have
occurred during an ice age with a warm ocean. If a
storm like the Pineapple Express storm occurred on
average once every four weeks with a precipitation
rate of 1,000 mm per week, a glacier 5,000 feet thick
would have developed in approximately 100 years.
Since precipitation rate is a function of sea-surface
temperature and storm frequency is a function of the
location of the jet stream, it would appear that the
presence of glaciers in Yosemite National Park during
an ice age can easily be explained by warm sea-surface
temperatures and a more southerly position of the jet
stream. Some melting of the glaciers would likely occur
depending on the length of the summers. Other types
of storms will also contribute to the growth of the
glaciers. The length of an ice age is also important to
the maximum depth of the glaciers. When additional
case studies are completed for other storm types, a
more detailed glacier model will be developed.

It is likely that Pineapple Express-like storms
coming from directions other than the southwest
like they do today could have also produced heavy
snowfall. For example, a consistent flow from the
west is common today, but does not produce large
accumulations of snow in the Sierra Nevada because
the underlying ocean surface is cold and large
quantities of moisture are not evaporated into the
atmosphere. If such continuous flow patterns from
the west, or even northwest, were to flow over a warm
Pacific Ocean, heavy accumulations like Pineapple
Express storms could have added significantly to the
annual snowpack.

Conclusions

A warm, tropical storm during the Christmas
holidays of 1996–1997 called the Pineapple Express
storm has been successfully simulated. Additional
simulations of warm sea-surface temperatures in
the eastern Pacific Ocean were conducted to find if
precipitation in Yosemite National Park would have
been increased. Warm sea-surface temperatures
doubled or quadrupled the precipitation in Yosemite
National Park and throughout the Sierra Nevada.
This enhanced snowfall and greater frequency of
storms appear to be adequate to explain glaciation in
the Sierra Nevada during an ice age in a young-earth
time frame. Glaciers thousands of feet thick could
have readily developed during hundreds of years
following the Genesis Flood.

Acknowledgments

The mesoscale meteorology model (WRF) used
in this study was developed and maintained by the
National Center for Atmospheric Research (NCAR)
available at http://www.wrf-model.org/index.php.
The meteorological and topographic data (NARR)
used in this study were provided by the National
Oceanographic and Atmospheric Administration
(NOAA) National Operational Model Archive &
Distribution System available online at http://www.emc.ncep.noaa.gov/mmb/rreanl/.
Richard Carpenter and Brent Shaw of Weather Decision Technologies,
Inc., and Valentine Anantharaj and Xingang Fan
of Mississippi State University offered occasional
assistance in the use of WRF. This research was
funded by the National Creation Research Foundation
of the Institute for Creation Research.

Answers Research Journal

2010 Volume 3

Cutting-edge creation research. Free. Answers Research Journal (ARJ) is a professional, peer-reviewed technical journal for the publication of interdisciplinary scientific and other relevant research from the perspective of the recent Creation and the global Flood within a biblical framework.

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Answers in Genesis is an apologetics ministry, dedicated to helping Christians defend their faith and proclaim the gospel of Jesus Christ effectively. We focus on providing answers to questions about the Bible—particularly the book of Genesis—regarding key issues such as creation, evolution, science, and the age of the earth.